The isoindole has been used, for instance, as a fluorescent labeling reagent, an antihypertensive agent, and a physiologically active substance, and it is known that the non-substituted form of the isoindole tends to decompose readily in air at the room temperature. Although such an isoindole has been utilized for the above mentioned uses even in its as-is form and its derivative form, polymer forms of the isoindole, i.e., pyrromethene has been used as a red organic EL (electroluminescence) material, and tetrabenzoporphyrin and phthalocyanine have been used as organic semiconductor, photosensitizer for photo dynamic therapy of cancer, solar cell material, and pigment, etc.
Non-patent literatures 1-3 can be enumerated as literatures which disclose the method of manufacturing the isoindole. Concretely, in the non-patent literatures 1 and 2, the condition of 500° C./0.01 mmHg or 600° C., and in the non-patent literature 3, the thermal decomposition condition of 230° C. with using diphenyl ether, are used respectively.    Non-patent literature 1: R. Bonnett and R. F. C. Brown, “Isoindole” Chem. Commun., 393-395, 1972    Non-patent literature 2: J. Bornstein, D. E. Remy and J. E. Shields, “Synthesis of isoindole by retro-Diels-Alder reaction” Chem. Commun., 1149-1150, 1972    Non-patent literature 3: H. Uno, S. Ito, M. Wada, H. Watanabe, M. Nagai, A. Hayashi, T. Murashima and N. Ono, “Synthesis and structures of pyrroles fused with rigid bicyclic ring systems at β-positions” J. Chem. Soc., Perkin Trans. 1, 4347-4355, 2000